(1) Field of the Invention
The present invention relates to an image display device, and in particular to an image display device having an image display panel, such as a liquid crystal panel or an organic electroluminescent panel, and a touch panel.
(2) Description of the Related Art
Thin image display devices, such as liquid crystal modules (liquid crystal display devices) and organic electroluminescent modules (organic EL display devices), are used for the display devices of many portable information apparatuses, such as cellular phones, personal data assistants (PDAs), digital cameras and multimedia players.
FIG. 1 is a perspective diagram showing an example of a liquid crystal display device that is formed of a liquid crystal panel and a backlight unit BLU for illuminating the liquid crystal panel. DA represents the display region of the liquid crystal panel. The liquid crystal panel has a TFT substrate (TFTS) on which switching elements made of thin film transistors and electrodes are provided and a color filter substrate (facing substrate, CFS) on which color filters are formed, and liquid crystal is sealed in between the TFT substrate and the color filter substrate. A driver chip (DRC) for driving the liquid crystal panel is mounted on part of the TFT substrate. In addition, the liquid crystal panel has an upper polarizing plate (UPP) provided on the upper side of the color filter substrate and a lower polarizing plate (not shown) provided on the lower side of the TFT substrate. Furthermore, the wires connected to the liquid crystal panel are included in a flexible printed circuit (FPC) as shown in FIG. 1. The organic EL display device also uses a TFT substrate where the wires are connected in an FPC.
Recently, image display devices having a touch panel have been proposed in order to make the operation of information apparatuses easier. FIG. 2 is a perspective diagram showing a touch panel where touch panel electrodes (TPE) are formed on one side of a touch panel substrate (transparent substrate, TPS). The wires connected to the touch panel are included in a flexible printed circuit (FPC) on which a driving IC for driving the touch panel is mounted. IFT represents the interface of the flexible printed circuit.
FIG. 3 shows an example of a liquid crystal display device having a touch panel. A front panel (FW) for protecting a liquid crystal panel LCP and a touch panel TP are provided, and the touch panel TP and the liquid crystal panel LCP are provided in this order on the rear surface. Thus, the touch panel and the liquid crystal panel are provided in proximity, and therefore there are many wires in a small space which makes it difficult to make the liquid crystal display device thinner. The same problem arises in organic EL display devices.
JP 2003-280541A discloses a number of liquid crystal panels that are implemented by using one flexible printed circuit in order to provide display devices on the two sides, front and rear. The present inventor examined the method for implementing a touch panel and a liquid crystal panel connected through one flexible printed circuit and found that there is no space for the backlight between the touch panel and the liquid crystal panel as in JP 2003-280541A. Therefore, the distance between the terminals for the liquid crystal panel on the flexible printed circuit and the terminals for the touch panel is short, which makes it difficult to connect the flexible printed circuit to the liquid crystal panel and the touch panel with high precision.
In addition, the connection between the flexible printed circuit and the liquid crystal panel (portion represented by FOG in FIG. 3) is made by an FOG contact bond where the two are connected through the application of pressure and heat with an anisotropic conductive film in between. Therefore, the flexible printed circuit is connected to one panel, and after that the flexible printed circuit is connected to the other panel when it is found that the previous connection might slide or disengage due to the heat applied for the FOG contact bond, which leads to a problem.
In addition, JP 2005-38231A discloses a touch panel attached to one branch of an FPC and a liquid crystal display device attached to the other branch in order to reduce the number of connection cables so that the cost for parts and cost for assembly can be reduced. Furthermore, JP 2005-38231A discloses a touch panel and a liquid crystal display device that are integrated.